Key concepts edexcel chemisty

Key concepts edexcel chemisty

1. Chemical Equations

   • can write them using words or symbols
     • methane burning in oxygen makes carbon dioxide and water: methane + oxygen -> carbon dioxide + water
     • magnesium and oxygen react to make magnesium oxide : 2Mg + O2 -> 2MgO
       • these must be balanced so they need to have the same number of atoms for each element
   • state symbols can be used next to each substance to see the physical state it is in
     • solid - (s)
     • liquid - (l)
     • gas - (g)
     • aqueous(dissolved in water) - (aq)
   • different ions and different formulas
     • ammonium - NH4^+
     • nitrate - NO3^-
     • sulfate - SO4^2-
     • hydroxide - OH^-
     • carbonate - CO3^2-
   • ionic equations just show the useful bits
     • they only show the reacting particles
     • to write an ionic equations just look at the balanced equation and take out any aqueous ions on both sides
     • example:

2. Hazards and Risks

   • a hazard is anything that has the potential to cause harm. the risk is the probability of someone getting hurt
     • hazards can come from equipment used or chemicals used

3. history of the atom

   • first atom structure
     • found by John Dalton at the start of the 19the century
     • described it as a solid sphere that is made up of different elements
   • second atom structure
     • found by JJ Thomas in 1897
     • he found out that atoms weren't solid spheres and contained smaller, negatively charged particels
     • know as the "plum pubbing model
   • third atom structure
     • found by Rutherford in 1909
     • they fired positively charged alpha particles at an extremely thin piece of gold
       • they where expecting it to travel straight through or be partially deflected,
       • more particles then expected where deflected and some where deflected backward so the plum pudding could be right
     • he came up with the nuclear atom, where there is a tiny positively charged nucleus surrounded by a "cloud" of negative electrons
   • fourth atom structure
     • found by Bohr
     • he realised that if the electrons where in a cloud they would be attracted to the nucleus and the atom would collapse
       • therefore electrons could only exist in fixed orbits, or shells and each shell has a fixed energy
     • out current view on the atom
   • last atom
     • found by James Chadwick
     • found the neutron
     • found in 1932

4. the atom

   • contains protons neutrons and electrons
     • protons
       • have a relative mass of 1 and a positive charge
     • neutrons
       • have a relative mass of 1 and a charge of 0
     • electrons
       • have a relative mass of 0 and a charge of -1
   • the nucleus
     • in the middle
     • contains protons and neutrons
     • has a positive charge
     • holds the mass
   • atomic and mass number
     • atomic number- tells you how many protons the atom has
     • mass number tells you the total number to protons and nuetrons
   • isotopes
     • these are different forms of the same element , they have the same number of protons but different number of neutrons
     • is an element has more then 1 isotope then the Ar is the average of the mass numbers of all the different isotopes
       • multiply each relative isotopic mass number by its isotopic abundance and add up results: boron-10 and boron-11 have an abundance of 4 and 16. (10x4)+(11x16)
         • then you divide this by the sum of the isotopic abundances. 216/(16+4)

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